A thermal instability in the non-relativistic planar magnetron

1990 ◽  
Vol 44 (3) ◽  
pp. 517-524 ◽  
Author(s):  
S. N. Antani ◽  
D. J. Kaup ◽  
G. E. Thomas
Keyword(s):  
Temperature Distribution ◽  
Numerical Simulations ◽  
Thermal Effects ◽  
Thermal Instability ◽  
Convective Cell ◽  
Electron Cloud ◽  
Analytic Calculation ◽  
Temperature Anisotropy ◽  
Anisotropic Temperature ◽  
Planar Magnetron

It is well known that an anisotropic temperature distribution gives rise to thermal instability in many Systems. In their numerical simulations of a two-vane, non-relativistic planar magnetron, Thomas et al. reported a temperature anisotropy and a concomitant formation and growth of a swirling electron cloud bunch (convective cell). In this paper we present an analytic calculation of the shift in the eigenfrequencies by treating the thermal effects as a perturbation, while taking due account of the temperature anisotropy. We find the magnitude of the resulting rate to be of the order of that seen in the simulations.

scholarly journals A TWO-DIMENSIONAL THERMODYNAMIC MODEL TO PREDICT HEART THERMAL RESPONSE DURING OPEN CHEST PROCEDURES

2016 ◽  
Vol 15 (1) ◽  
pp. 44
Author(s):  
F. G. Dias ◽  
J. V. C. Vargas ◽  
M. L. Brioschi
Keyword(s):  
Cardiac Surgery ◽  
Temperature Distribution ◽  
Thermodynamic Model ◽  
Thermal Effects ◽  
Computational Simulation ◽  
Thermal Response ◽  
Cardiac Response ◽  
The Finite Element Method ◽  
Thermal Distribution ◽  
Open Chest

In this work, the temperature distribution of the heart in an open chest surgery scenario is studied. It is also evaluated the cardiac thermal effects of the injection of a cooling liquid in the aorta root, which is used in infrared thermography. The finite element method was used to develop a model that predicts the temperature distribution modification in a 2-dimensional slice of the heart. This thermodynamic model allows the computational simulation of the thermal cardiac response to open chest procedures, which are required by cardiac surgery. The influence of several operating parameters (e.g., coronary flow rate, temperature) on the resulting thermal distribution is analyzed. Therefore, this analysis allows the identification of parameters that could be controlled to minimize the loss of energy, and consequently, avoiding the hazardous thermal distribution that could put the heart in danger during cardiac surgery.

scholarly journals Numerical modelling approach for the temperature dependent forming behaviour of Ti-6Al-4V

2018 ◽  
Vol 190 ◽  
pp. 12004
Author(s):  
Thomas Papke ◽  
Matthias Graser ◽  
Marion Merklein
Keyword(s):  
Elevated Temperature ◽  
Temperature Distribution ◽  
Numerical Modelling ◽  
Tensile Test ◽  
Numerical Simulations ◽  
Numerical Models ◽  
Uniaxial Tensile ◽  
Temperature Dependent ◽  
Inhomogeneous Temperature ◽  
Forming Behaviour

Titanium alloys offer several beneficial characteristics, such as high specific strength, metallurgical stability at elevated temperature, biocompatibility and corrosion resistance. With regard to these superior properties, Ti-6Al-4V is a commonly used titanium alloy for aerospace components and medical products. The production of parts made of Ti-6Al-4V can be done in various ways. One approach is forming at elevated temperature, which requires a focused design of parts, processes and numerical modelling of the forming process. Essential input parameters for the numerical models are temperature dependent material parameters. Since, the yield stress and Young's modulus of the material decrease significantly at elevated temperature, the forming limits are enhanced. For the characterization of the forming behaviour, uniaxial tensile tests at temperatures from 250 °C to 400 °C have been conducted. The samples are heated by conduction in a thermal-mechanical simulator for the tensile test. However, the resulting inhomogeneous temperature distribution along the longitudinal axis of the specimen is a challenge in order to measure proper material properties. Inhomogeneous temperature distribution leads to varying mechanical properties and temperature dependent forming behaviour. To overcome this issue, simple numerical models based on experimental data are necessary, which allow the estimation of the influence of the inhomogeneous temperature distribution. In this paper, therefore, the temperature distribution and the subsequent tensile test are investigated using electrical-thermal and mechanical numerical simulations of the tensile test at elevated temperature. With the combined approach of experimental tests and numerical simulations, the forming behaviour of Ti-6Al-4V can be modelled.

Thermal instability in a star—gas system

1995 ◽  
Vol 54 (2) ◽  
pp. 157-172 ◽  
Author(s):  
S. P. Talwar ◽  
M. P. Bora
Keyword(s):  
Heat Loss ◽  
Thermal Effects ◽  
Thermal Instability ◽  
Composite System ◽  
Stellar Dynamics ◽  
Mhd Equations ◽  
Temperature Dependent ◽  
Gas System ◽  
The Stability ◽  
Loss Mechanisms

A composite interstellar model consisting of stars and optically thin radiating plasma is considered in order to investigate the thermal instability arising from possible radiation and other heat-loss mechanisms. The stellar dynamics is governed by the Vlasov equation, while the gas is supposed to be a hydromagnetic plasma, described by the MHD equations, with a density- and temperature-dependent heat-loss function. It is shown that while with cold stars the system is in general unstable irrespective of thermal effects of the plasma, with warm stars having a Maxwellian distribution the thermal plasma considerably influences the stability of the composite system. It is also shown that the otherwise stable composite (with warm stars) configuration may become unstable in the presence of a radiating plasma because of coupling between the heat-loss mechanisms and stellar populations.

Thermal effect on large-aspect-ratio Couette–Taylor system: numerical simulations

2015 ◽  
Vol 771 ◽  
pp. 57-78 ◽  
Author(s):  
Changwoo Kang ◽  
Kyung-Soo Yang ◽  
Innocent Mutabazi
Keyword(s):  
Heat Transfer ◽  
Temperature Gradient ◽  
Aspect Ratio ◽  
Numerical Simulations ◽  
Convective Cell ◽  
Base Flow ◽  
Large Aspect Ratio ◽  
Radial Temperature ◽  
Instability Modes ◽  
Momentum And Heat Transfer

We have performed numerical simulations of the flow in a large-aspect-ratio Couette–Taylor system with rotating inner cylinder and with a radial temperature gradient. The aspect ratio was chosen in such a way that the base state is in the conduction regime. Away from the endplates, the base flow is a superposition of an azimuthal flow induced by rotation and an axial flow (large convective cell) induced by the temperature gradient. For a fixed rotation rate of the inner cylinder in the subcritical laminar regime, the increase of the temperature difference imposed on the annulus destabilizes the convective cell to give rise to co-rotating vortices as primary instability modes and to counter-rotating vortices as secondary instability modes. The space–time properties of these vortices have been computed, together with the momentum and heat transfer coefficients. The temperature gradient enhances the momentum and heat transfer in the flow independently of its sign.

SINGLE-ELECTRON CIRCUITS PERFORMING DENDRITIC PATTERN FORMATION WITH NATURE-INSPIRED CELLULAR AUTOMATA

2007 ◽  
Vol 17 (10) ◽  
pp. 3651-3655 ◽  
Author(s):  
TAKAHIDE OYA ◽  
IKUKO N. MOTOIKE ◽  
TETSUYA ASAI
Keyword(s):  
Pattern Formation ◽  
Cellular Automata ◽  
Physical Properties ◽  
Cellular Automaton ◽  
Numerical Simulations ◽  
Thermal Effects ◽  
Semiconductor Device ◽  
Single Electron ◽  
Dendritic Trees ◽  
Single Electron Devices

We propose a novel semiconductor device in which electronic-analogue dendritic trees grow on multilayer single-electron circuits. A simple cellular-automaton circuit was designed for generating dendritic patterns by utilizing the physical properties of single-electron devices, i.e. quantum and thermal effects in tunneling junctions. We demonstrate typical operations of the proposed circuit through extensive numerical simulations.

Analysis of Microheat Pipes With Axial Conduction in the Solid Wall

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Yew Mun Hung ◽  
Kek-Kiong Tio
Keyword(s):  
Temperature Distribution ◽  
Heat Transport ◽  
Thermal Effects ◽  
Solid Wall ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Working Fluid ◽  
Transport Capacity ◽  
Axial Temperature ◽  
Energy Equations

A one-dimensional, steady-state model of a triangular microheat pipe (MHP) is developed, with the main purpose of investigating the thermal effects of the solid wall on the heat transport capacity of an MHP. The energy equation of the solid wall is solved analytically to obtain the axial temperature distribution, the average of which over the entire length of the MHP is simply its operating temperature. Next, the liquid phase is coupled with the solid wall by a heat transfer coefficient. Then, the continuity, momentum, and energy equations of the liquid and vapor phases are, together with the Young–Laplace equation, solved numerically to yield the heat and fluid flow characteristics of the MHP. The heat transport capacity and the associated optimal charge level of the working fluid are predicted for different operating conditions. Comparison between the models with and without a solid wall reveals that the presence of the solid wall induces a change in the phase change heat transport by the working fluid, besides facilitating axial heat conduction in the solid wall. The analysis also highlights the effects of the thickness and thermal conductivity of the solid wall on its axial temperature distribution. Finally, while the contribution of the thermal effects of the solid wall on the heat transport capacity of the MHP is usually not dominant, it is, nevertheless, not negligible either.

LARGE SCALE ANISOTROPY OF MICROWAVE BACKGROUND RADIATION IN ROTATING COSMOLOGIES

1995 ◽  
Vol 04 (01) ◽  
pp. 161-165 ◽  
Author(s):  
V.N. PAVELKIN ◽  
V.F. PANOV
Keyword(s):  
Temperature Distribution ◽  
Large Scale ◽  
Background Radiation ◽  
Null Geodesic ◽  
Radiation Temperature ◽  
Geometric Optics ◽  
Temperature Anisotropy ◽  
Microwave Background ◽  
Microwave Background Radiation ◽  
Observation Position

The background radiation temperature distribution as a function of observation position angles for Gödel type cosmologies with expansion, rotation and shear is studied in the geometric optics approach. Null geodesic equations in the relevant metrics are solved for some particular cases and the background radiation temperature anisotropy for two directions is evaluated in terms of the values of rotation and shear.

Sign in / Sign up

Export Citation Format

Share Document